This invention relates to polymer foams containing nanoclay, more particularly to improvements in the properties of polymeric foams by dispersing nanoclay into the polymer foam compositions.
CFC (chiorofluorocarbon) foam blowing agents such as CFC-11 and CFC-12 provide rigid foams with excellent insulation properties, dimensional stability and fire performance. The use of CFCs has been phased out, however, because they are considered to be detrimental to the ozone layer. The blowing agent alternatives now in use for polymer foams, HCFCs (hydrochlorofluorocarbons), HFCs (hydrofluorocarbons) and HCs (hydrocarbons), generally can not achieve foams having similar properties. For example, the insulation properties are generally poorer because the alternative blowing agents have higher thermal conductivity than CFCs.
It would therefore be useful to provide the industry with a means of improving polymer foams, especially in terms of insulation values.
Polymer foam compositions, such as polyuirethane foam compositions, are provided which comprise up to about 10 weight % of nanoclay dispersed therein, based on total polymer weight, as well as the resulting polymer foams.
It has now been found that integration of nanoclay into the polymer foam composition results in foams having improved properties. Not only are thermal insulation properties improved (both in terms of initial and aged k-factors), but the resulting foams have a fine cell structure, believed to result from the nanoclay acting as a nucleating agent in the foam process. The slow aging rate of the foams suggests that the nanoclay also acts as a gas barrier reducing the infusion of air into the foam cells and diffusion of the blowing agents out of the foam cells.
Nanoclays (nanosized clays) are plate-like materials, the clay mineral being generally selected from smectite, vermiculite and halloysite clays. The smectite clay in turn can be selected from montmorillonite, saponite, beidellite, nontrite, hectorite and mixtures thereof. A preferred clay mineral is the montmorillonite clay, a layered alumino-silicate. The nanoclay platelets generally have a thickness of about 3-1000 Angstroms and a size in the planar direction ranging from about 0.01 micron to 100 microns. The aspect ratio (length versus thickness) is generally in the order of 10 to 10,000. These clay platelets are separated by a gallery, a space between parallel layers of clay platelets containing various ions holding platelets together. One such material is Cloisite(copyright) 10A (available from Southern Clay Products), its platelets having a thickness of about 0.001 micron (10 Angstroms) and a size in the planar direction of about 0.15 to 0.20 micron.
The invention is applicable to both thermoset and thermoplastic polymer foams. Thermoset polymers include polyurethane, polyisocyanurate and phenolic resins, while thermoplastics include polystyrene, polypropylene, polyethylene and polyvinyl chloride resins.
Any conventional blowing agent can be used, such as HFCs, HCFCs, HCs or mixtures thereof. HCFC-141b (1,1-dichloro-1-fluoroethane) is illustrated in the example below.
The nanoclay should be dispersed uniformly in one or more components of the polymer foam composition. This may be done by conventional techniques such as milling or extruding. Or, as in the example below, the nanoclay can be dispersed into the blowing agent using an ultrasonic water bath.
The amount of nanoclay generally ranges from about 0.01 part to about 10 parts of 100 parts by weight of total (polymer) resin.
The other components of the foam formulations may be those which are conventionally used, which components and their proportions are well known to those skilled in the art.